In many applications it is desirable for a user to remotely control the operation of a slave device by means of a hand-controller--a device which senses the movement of a handle gripped by the user's hand and generates one or more control signals which, in turn, are used in directing the actuation of the slave device. Hand controllers are commonly used in applications where the user is necessarily in a location which is remote from the slave, for example, where the slave is in a hazardous environment, such as an environment where high levels of radiation are present. Hand controllers are also well suited for teleoperation in environments where direct viewing is limited. Examples include murky underwater environments with reduced light and obstructions such as underground excavation applications. To improve the sensitivity of the user to the slave's environment, a force-feedback system can be used to reflect the forces generated on the hand back to the user via the hand controller. For instance, if the slave unit impacts an object, the force of the impact is felt by the user's hand.
Force reflecting hand controllers for tele-operation are well known. Units which reflect the force sensed by a remote manipulator are disclosed in U.S. Pat. Nos. 4,837,734 to Ichikawa et al., 4,853,874 to Iwamoto et al., 4,888,538 to Dimitrov et al., 4,893,981 and 5,018,922 to Yoshinada et al., 4,942,538 to Yuan et al., 5,004,391 to Burdea, and 5,053,975 to Tsuchihashi et al. These units use electrical force feedback, usually applied through an electric motor/gear drive, to present the forces sensed by a remote manipulator to the user.
FIG. 1 summarizes the basic operation of prior art devices. The position, velocity, and/or acceleration provided on a master hand controller 10 on a handle 12 by a user (not shown) is sensed and transmitted as a command by a controller 14 to move the slave device 16. In turn, the actual position, velocity, and/or acceleration is read from the slave device 16 and is sent back by the controller 14 as a command to the master hand controller 10, providing the user with direct kinesthetic feedback from the remote device he is controlling.
To simplify control, many prior art devices are a kinematically similar replica of the remote device under control. This kinematic similarity reduces or eliminates the need for a computer controlled interface between the master hand controller unit and the remote slave device. This kinematic similarity requires a unique hand-controller for each unique slave device. Changes made to the kinematics of the slave device require similar changes to the controller.
Prior force reflecting hand controller configurations have used either counter weights or active compensation to remove friction and gravity effects from the controller handle. The use of counterweights increases the mass and moment of inertia of the system which, in turn, increases user reaction time due to the additional forces necessary to accelerate and decelerate the handle. Active gravity compensation increases the complexity of a system while simultaneously increasing the possibility of undesirable system instability.
Further, by reacting to remote forces present on a slave device, the prior art devices lack the capability of creating a three-dimensional tactile virtual reality environment whereby a user's actions and reactions are related to a simulated world such as simulations of driving or flying functions, simulation of molecular force interactions, or simulations of surgical procedures. U.S. Pat. No. 5,044,956 to Behensky et al. discloses a system whereby a steering wheel is used to input positions to a simulation which in turns actuates the wheel in response to simulated artifacts. This system does not disclose or anticipate the simulation and coordination of the six-degrees of freedom required for the arbitrary positioning and orientation of solid objects. Similarly, prior art devices which simulate virtual reality by visual feedback to a user are not capable of accepting tactile inputs and providing tactile force feedback.